Deep brain stimulation (DBS) and other related procedures involving implantation of leads and catheters are increasingly used to treat Parkinson's disease, dystonia, essential tremor, seizure disorders, obesity, depression, restoration of motor control, and other debilitating diseases. During these procedures, a catheter, lead, or other medical device is strategically placed at a target site in the brain. Locating the “best” target for stimulation in the brain can be a painstaking procedure.
Implantation of a lead for DBS generally involves the following preliminary steps: (a) anatomical mapping and (b) physiological mapping. Anatomical mapping involves mapping segments of an individual's brain anatomy using non-invasive imaging techniques, such as magnetic resonance imaging (MRI) and computed axial tomography (CAT) scans. Physiological mapping involves localizing the brain site to be stimulated. Step (b) can be further divided into: (i) preliminarily identifying a promising brain site by recording individual cell activity with a microelectrode and (ii) confirming physiological stimulation efficacy of that site by performing a test stimulation with a macroelectrode or microelectrode, however a macroelectrode is preferred.
Microelectrode recording is generally performed with a small diameter electrode with a relatively small surface area optimal for recording single cell activity. The microelectrode may be essentially a wire which has at least the distal portion uninsulated to receive electrical signals. The rest of the body or wire of the microelectrode may be insulated. The microelectrode functions as a probe to locate a promising brain site. Since a number of attempts may be required to locate the precise target site, it is desirable that the microelectrode be as small as possible to minimize trauma when the microelectrode is placed into the brain, in some cases, multiple times.
Once a brain site has been identified, a macroelectrode is used to test that the applied stimulation has the intended therapeutic effect. Once macrostimulation confirms that stimulation at the brain site provides the intended therapeutic effect, the macroelectrode is withdrawn from the brain and a DBS lead is permanently implanted at the exact site.
A conventional procedure for carrying out the microelectrode recording phase of DBS may involve the following detailed steps: (1) placing a stereotactic frame on the subject, which stereotactic frame is a device temporarily mounted on the head to assist in guiding the lead system into the brain; (2) performing MRI or equivalent imaging of the subject with the stereotactic frame; (3) identifying a theoretical target using a planning software; (4) placing the subject with the stereotactic frame in a head rest; (5) using scalp clips, cutting the subject's skin flap in the head, exposing the working surface area of the cranium; (6) placing the stereotactic arc with target coordinate settings and identifying the location on the skull for creation of a burr hole; (7) removing the arc and drilling a burr hole in the patient's skull; (8) placing the base of the lead anchor; and (9) with the microelectrode recording drive attached, and with an appropriate stereotactic frame adaptor inserted into the instrument guide, placing the stereotactic arc.
Next, (10) advancing a microelectrode cannula (or several at a time) and an insertion rod into the brain until they are approximately 25-35 mm above the target; (11) removing the insertion rod, and leaving the cannula in place; (12) inserting a recording microelectrode such that the tip of the microelectrode is flush with the tip of the microelectrode cannula; (13) connecting the connector pin of the recording microelectrode to a microelectrode recording system; (14) starting approximately 25 mm above the target, advancing the microelectrode into a recording tract at the specified rate using the microdrive; and (15) if the target is identified, removing the recording microelectrode cannula and recording microelectrode and leaving a stimulation or recording lead or similar device in their place.
Some physicians might use additional steps, fewer steps, or perform the steps in a different order.
On average, a single microelectrode recording tract takes approximately 30 minutes to perform. Each microelectrode recording tract requires placement of a larger diameter insertion cannula at a distance of 25-35 mm above the target site through viable brain tissue. Each time an object is inserted into the brain there is approximately a 5% risk of hemorrhage. Creating multiple tracts increases the risk for intracranial bleeding, duration of operation, post-operative infection, and operative risk. Creating new tracts is fraught with misalignment/misplacement problems because the introduction cannulas may not trace the exact pathways desired.
There is, therefore, a need to provide a system and method for implanting a medical device such as a lead into the brain that reduces the duration of the operation, reduces the number of repetitive invasive tracts created to find the “best” target site, reduces post-operative infection, and reduces operative risk to provide optimal physiological therapy.